1. Field of the Invention
The present invention relates to an antenna of a mobile communication terminal, and more particularly to an antenna of a mobile communication terminal capable of maintaining a length of a required conductor line and improving the average radiation gain of the antenna even when a length of the antenna is structured to be short.
2. Description of the Prior Art
In recent years, as a mobile communication terminal such as cellular phone and PDA phone has been widely used, an antenna for the mobile communication terminal, which receives/transmits radio waves, has made remarkable progress. In the drawings, FIG. 1 is a schematic view of a helical antenna of a mobile communication terminal having a main radiator according to the prior art, and FIG. 2 is a schematic view of a PCB type antenna of a mobile communication terminal having a main radiator according to the prior art.
As shown in FIG. 1, a helical antenna 10, which is an external antenna, comprises a metal part 11 supplying a signal to the antenna 10, a coil 13 connected to the metal part 11 and determining a resonance property of the antenna 10, and a plastic injection 15 surrounding and fixing the coil 13.
A resonance of the antenna occurs by a pitch (P) of the coil 13 and a relative dielectric constant of a plate-shaped dielectric that is the plastic injection 15 and the resonance property of the antenna appears at bands of 900 MHz and 1,800 MHz.
In the mean time, as shown in FIG. 2, a PCB type antenna 20, which is an external antenna, comprises a plate-shaped dielectric 23 and a conductor line 21 which is formed into a continuously curved shape on an upper part of the plate-shaped dielectric 23, and is mounted to an exterior of a mobile communication terminal with being surrounded by a plastic injection (not shown).
Since the above external antennas are outwardly protruded from the mobile communication terminal, it is very inconvenient for a user to carry it. Accordingly, in order to solve the inconvenience, a length of the external antenna should be shortened to the utmost.
There is no choice but to reduce the pitch (P) so as to shorten the length of the antenna while maintaining a length of the coil or conductor line according to frequency bands. However, the emissivity of the antenna is determined by the pitch of the coil and the conductor line. Accordingly, when the pitch (P) of the coil or conductor line is reduced so as to shorten the length of the antenna, the emissivity is proportionally decreased and thus it is impossible to obtain a desired property of the antenna.
In addition, ends of the coil of the above helical antenna and the conductor line of the PCB type antenna are located at an upper end of the antenna. With the mobile communication terminal having the prior external antenna, when a user grasps the mobile communication terminal and performs a call, the end of the antenna is surrounded or screened by a hand or object in many cases. Since charges are concentrically gathered at the end of the antenna, radiation of electromagnetic waves is hindered when the end of the antenna is screened. In addition, a property of a stationary wave is drastically decreased due to movement of a resonant frequency at GSM900 or GSM850 having a relatively narrow bandwidth.